Method of preparing ammoniated nitric acid-phosphate rock extracts



Nov. 11.1969 A. v. SLACK 3, 77,843

METHOD OF PREPARING AMMONIATED NITRIC ACID-PHOSPHATE ROCK EXTRACTS FiledJan. 16, 1967 8 Sheets-Sheet 1 OF PREPARATION o-NEUTRAL CITRATE METHOD(A.b.A.c.) O-ALKALINE CITRATE METHOD P205 AVAILABILITY,

ANALYSES MADE WITHIN IWEEK NOTE: ll-3T-0 WAS ADDED AT pH 2.3 T0

2.5 DURlNG AMMONIATION STEP FINAL pH 7.0 T0 8.5.

o l I l A 5 IO [5 P205 FROM ll-37-0. OF TOTAL P205 L l 1 l l 1 l C00:P205 MOLE'RATIO (AFTER u-sr-o ADDITION) EFFECT OF Il-37-O ADDITIVE ONAVAILABILITY OF P 0 IN NEUTRAL NITRIC PHOSPHATE SUSPENSIONS Fjg, 1

NOV. 11, 1969 v. SLACK 3,477,843

METHOD OF PREPARING AMMONIATED NITRIC ACID-PHOSPHATE ROCK EXTRACTS FiledJan. 16. 1967 8 Sheets-Sheet 2 s u N t A 1 60 '3 P205 SOLUBILITY:Q-NEUTRAL CITRATE 4O A-ALKALINE CITRATE III-WATER SOLUBLE y lI-BT-OADDED IN PROPORTION EQUAL TO 15% OF TOTAL P205 20 ,n

I I u L! U 0 v L5 2.0 2.5 I 3.0 3.5 4.0 4.5

pH AT TIME OF ADDITION OF II-37-O EFFECT OF II-3T-O, ADDED AT VARIOUS pHLEVELS, ON SOLUBILITY OF P 0 IN NITRIC PHOSPHATESUSPENSIONS AMMONIATEDTO pH 8.3 T0 8.5

F ig. 2

M INVENTOR.

Nov. 11, 1969 ACID-PHOSPHATE ROCK EXTRACTS Filed Jan. 16. 1967 8Sheets-Sheet 3 V: n n u n. M m B m w m 0 O X 6 4 S S Y 8 6 B .l E E l 3T 5 M m 2 m w T W P A M C C E R R L E E A m A LNL R L P 000 T A A 2 M NM w m M l O z 5 N A N M D W w M B m vw .m DO T M a O n. M HAC A .0 ED OMMM m. mm .N M MF 3 x0 .\\\DY N rlllll II I l Illlll'l-lllnllmllwlullllvlllllll 9.5m .EMGGB O a 2 .3 0 0 00 m 8 4 O W w 6M 2 In ef 25.? 6 Pzwumwm N: P205 WEIGHT RATIO Nov. 11, 1969 A. v. SLACKMETHOD OF PREPARING AMMONIATED NITRIC ACID-PHOSPHATE ROCK EXTRACTS 8Sheets-Sheet 4 Filed Jan. 16. 1967 m Y 2 Y. n P T L L II II Y m m w M Lo 0 .ll U o .T M S X 2 2 v v W S m m 0 E n m m m M m M 2 A R n T 2 m R WC P E C T E u M n 3 o L I. T M m N m 3 IT K A w E mm U L C V 2 E A l P NN 3" a m o nu 0 A m M M M 1\ fi o \A D Z T mm oEE .Ewm; o x of z :2 MNMA X0 0 0 2 O O Q 0 w 8 6 4. 0 8 6 4 2 I of 45.0... 6 .Euomma 0.6 0.8NH; m0; MOLE RATIO N :P 0 WEIGHT RATIO WITHOUT POLYPHOSPHATE (TE ST 99)Nov. 11, 1969 A. v. SLACK 3,477,843

METHOD OF PREPARING AMMONIATED NITRIC ACID-PHOSPHATE ROCK EXTRACTS FiledJan. 16, 1967 8 Sheets-Sheet 0 I F I 8 fr I Q I 6. 3 x IMMEDIATE I 6 0AFTER I DAY a? 4 I I l u-sv-o ADDED AT [THIS POINT| (A) NEUTRAL CITRATESOLUBILITY (B) ALKALINE CITRATE SOLUBILITY A (C) NONAPATITE P 0 (BYX-RAY) 0.4 0.6 0.9 L0 wa N03 MOLE RATIO PERCENT OF TOTAL P205 4 I 1 I0.9 L0 L1 1.2

N: P O WEIGHT RATIO AMMONIATION OF I:I:I RATIO NITRIC PHOSPHATESUSPENSION WITH POLYPHOSPHATE (TEST I00) HNO3: COO MOLE RATIO 2.0

ADDITIVES: II-37-O (15% OF TOTAL P205) KCI coo; P205 MOLE RATIO 3.|o

M3 W INVENTOR.

BY W

Nov. 11; 1969 Filed Jan. 16. 1967 PERCENT OF TOTAL P205 A. v. SLACK3,477,843 METHOD OF PREPARING AMMONIATED NITRIC ACID-PHOSPHATE ROCKBX'IRACTS 8 Sheets-Sheet I I x IMMEDIATE a o AFTER 1 DAY A I a )2 v I f"2 HNO :CaO MOLE RATIO= L86 1 ADDITIVE: 93 u sonso LBJTON 0 OFSUSPENSION; ADDED WITH HNO3) loo (coo-s0 P205 MOLE RATIO= 3.26

D (A) NEUTRAL CITRATE SOLUBILITY I 80 9 n I U (a) ALKALINE CITRATESOLUBILITY K I I U 8| '1 40 ii (c) NONAPATITE P205 (BY x-RAYI I I NOTE:ANALYSES MADE I TO 2 DAYS AFTER PREPARATION I I I NH3: N03 MOLE RATIO Il I l l 0.9 L0 Ll L2 L3 N: P O WEIGHT RATIO AMMONIATION OF NITRICACID-PHOSPHATE ROCK EXTRACT WITH SULFURIC ACID ADDITIVE (TEST I08) Fig.7

Nov. 11, 1969 A. v. SLACK 3,477,843

METHOD OF PREPARING AMMONIATED NITRIC ACID-PHOSPHATE ROCK EXTRACTS FiledJan. 16, 1967 8 Sheets-Sheet RELATIVE YIELD,

ADDITIVE lI-37-O NONE ALK. CITRATE SOL'Y, 90 4| RESPONSE OF CORN TONITRIC PHOSPHATE SUSPENSIONS (SPRAY TYPE APPLICATION) Fig. 8

United. States Patent Oifice METHOD OF PREPARING AMMONIATED NITRICACID-PHOSPHATE ROCK EXTRACTS Archie V. Slack, Sheffield, Ala., assignorto Tennessee Valley Authority, a corporation of the United States FiledJan. 16, 1967, Ser. No. 609,558 Int. Cl. C01b 25/32 US. CI. 71-39 8Claims ABSTRACT OF THE DISCLOSURE A method is described whereby theammoniation characteristics of nitric acid extracts of phosphate rockare improved, such ammoniation characteristics being of considerableimportance in connection with the manufacture of certain fertilizermaterials. The salient feature of the invention is the addition of arelatively small proportion of one or more soluble acyclic polyphosphatecompounds to the extract after ammoniation has been carried to partialcompletion (pH 1.9-2.5). Such addition effectively inhibits theformation of apatite, or other compounds more basic than dicalciumphosphate, during the subsequent completion of ammoniation toneutrality. With use of such inhibitor, in accordance with the methodsspecified, the final neutralized extract contains its phosphate valuesalmost exclusively as dicalcium phosphate, a compound that is much morereadily assimilable by growing plants than are the more basicphosphates.

The invention herein described may be manufactured and used by or forthe Government for governmental purposes without payment to me of anyroyalty thereon.

My invention relates to an improvement in certain characteristics ofnitric acid-phosphate rock extracts, particularly the ammoniationcharacteristics thereof, and more particularly to an improved method ofhandling nitric acid-phosphate rock extracts such that during thesubsequent ammoniation thereof I am able to inhibit the undesirableformation of apatite and other phosphate compounds that are unavailableas nutrient to growing plants. Still more particularly my inventionrelates to an improved method of ammoniating nitric acid-phosphate rockextracts through the use of a material which is believed to act as areaction inhibitor such that the subsequent ammoniation to neutrality ofextracts treated therewith results in precipitation of the P valuestherein almost exclusively as dicalcium phosphate-a compound that isrecognized as a highly effective source of phosphorus for growingplants-which improved process substantially eliminates, duringammoniation of such extracts to neutrality, the precipitation of largeproportions of the phosphorus values therein as apatite compounds inwhich the phosphorus is relatively unavailable as a nu trient forgrowing plants. I have found that the acid-rock extract ammoniated toneutrality after addition of the reaction inhibitor, according to myprocedure, is useful as a suspension-type fertilizer; further, that theP 0 values in the resulting suspension have been shown to be highlysoluble in both neutral and alkaline citrate solutions which areaccepted indications of high agronomic value; and further, that the P 0values, in greenhouse growth tests, are highly effective as fertilizerand are superior in this respect to the P 0 values in neutral suspensionmade without use of the reaction inhibitor. Finally, I have found thatthe suspension has good keeping qualities when sufficient reactioninhibitor material is used.

Heretofore it has been the practice in the chemical fertilizer industryto obtain phosphorus--one of the three principal plant neutrientsbyeither producing elemental phosphorus by the thermal treatment ofphosphate rock 31,477,843 Patented Nov. 11, 1969 in combination withcarbon and silicon whereby the smelting thereof produces elementalphosphorus vapors which are condensed and collected under water, arelatively expensive form of the plant nutrient, or by a relatively moreeconomical method of winning by chemical means the phosphorus valuesfrom phosphorus ore. My invention relates particularly to this secondand generally more economically attractive method of winning thephosphorus values from the phosphorus ore. Although this second methodis generally accepted to be more economically attractive, it,unfortunately, is beset with certain chemical engineering problemswhich, in the past, have tended to somewhat offset the otherwise moreeconomically attractive characteristics thereof. Of these severalproblems which have beset chemical engineers in the past, perhaps theone of greatest significance relates to the nature of the phosphorus orefrom which it is desired to win the P 0 values therefrom.

The phosphorus in most commercial phosphate ores is present largely asthe mineral fiuorapatite [Ca F (PO CaO:P O mole ratio=3], a form fromwhich it is not readily assimilated by growing plants. In preparation ofphosphate fertilizers, it is common practice to subject the ore to sometreatment or series of treatments that first decomposes the apatitecompound and then converts the phosphorus to compounds from which it canbe readily assimilated by growing plant systems. A common method ofdecomposing the apatite is treatment with mineral acids. Any of severalacids can be used; however, it is often economically advantageous toemploy nitric acid. Processes in which nitric acid is employed arecommonly referred to as nitric phosphate processes and the resultantproducts usually are referred to as nitric phosphates (solid products)or nitric phosphate suspensions (suspensiontype fertilizers).

The reaction of phosphate rock with nitric acid results in dissolutionof essentially all the calcium and phosphorus as well as most impuritiesin the ore. The solute of the resultant solution consists chiefly ofcalcium nitrate and phosphoric acid plus small amounts of fluorine andvarious other impurities from the rock. Such an extract solution ishighly acidic and highly corrosive and therefore is generallyundesirable either for direct use as a fluid-type fertilizer or as anintermediate material to be dried to form a solid-type fertilizer. Itis, therefore, common practice to introduce ammonia into the acid-rockextract solution to neutralize the acidity of the extract. Suchintroduction of ammonia also is of considerable economic advantage,since ammonia is the lowest cost form of nitrogen fertilizer.

As ammonia is introduced into nitric acid-phosphate rock extract,various chemical reactions occur which result in the precipitation ofsolid calcium phosphate compounds. It is well known, from previousexperiments, that during the course of progressive ammoniation of suchextract, the major solid phosphate that precipitates initially isdicalcium phosphate (CaHPO CaO:P 0 ratio=2) a highly effective solidfertilizer compound. As ammoniation progresses, continued precipitationof essentially pure dicalcium phosphate occurs until such time asapproximately percent of the phosphorus has been precipitated. At thispoint, however, the resultant slurry is still too acidic (pH about 2.3),and too corrosive, to be desirable as a suspension-type fertilizer.Also, for processing into solid fertilizers by drying, the slurry is notsatisfactory at this point because it contains, in solution, considerable amounts of calcium nitrate, the presence of which in a solidnitric phosphate would drastically increase the hygroscopicity of theproduct. Continued ammoniation of the extract to neutrality or nearneutrality overcomes the corrosive nature of the slurry but,unfortunately, has a very undesirable effect on the nature of theprecipitated phosphate compound. Not only does the remaining 10 percentof the P precipitate from the extract largely as unavailable apatite,but also a large proportion of the previously precipitated dicalciumphosphate reacts with soluble calcium in the extract and is thusconverted to undesirable apatite. The resultant neutral slurry thereforedoes not have satisfactory fertilizer value for direct use as asuspension fertilizer or for processing into solid form.

In solid nitric phosphate processes, it is common practice to minimizethe formation of apatite and simultaneously eliminate calcium nitrate byadjusting the CaO:P O mole ratio in the acid-rock extract to about 2(the stoichiometric ratio for formation of dicalcium phosphate) prior toammoniation. Such adjustment is often effected by introducing phosphoricacid. Usually, the phosphoric acid is mixed wtih the nitric acid priorto extraction of the rock; in this manner, the acidulating value of thephosphoric acid is utilized and the nitric acid requirement is reduced.For adjustment of CaO:P O ratio to 2, the amount of P 0 required as acidis about 80 percent as much as that obtained from the rock, thusconsiderable expense is entailed in making adjustment by this method.Another common method of adjustment is the introduction of a solublesulfate such as sulfuric acid or potassium sulfate. Such procedureresults in removal (precipitation) of calcium from solution as thesulfate and consequent altering of the CaO:P O ratio to 2. A seriousdisadvantage of this method of adjustment, however, is a lowering of thegrade of the final product because of the dilution effect of the calciumsulfate.

In the preparation of nitric phosphate suspension-type fertilizers,adjustment of the CaO:P O mole ratio to 2.0 by the above methods may beused as a means of permitting ammoniation to neutrality withoutformation of apatite or other relatively unavailable phosphatecompounds. However, the other effect of adjustment, the elimination ofcalcium nitrate, is of no importance in the case of suspension-typefertilizers. Furthermore, both of the methods for adjustment describedabove have very serious disadvantages when applied to suspensionfertilizers. With the first method, the amount of phosphoric acidrequired is so great that the economic advantage of the suspensionprocess is largely dissipated. In the case of adjustment with sulfuricacid, the lowering of the grade of the product is considerable withresultant increases in handling and distribution costs. Also, we findthat in the case of neutral suspension fertilizers, the use of sulfateadditive does not prevent conversion of an excessive proportion of the P0 value to apatite, which apatite is of little or no agronomic value.

In view of the disadvantages of adjusting CaO:P O mole ratio to 2 inpreparation of suspension-type nitric phosphate fertilizers, it would beof considerable value to have available a method by which unadjustedextract could be ammoniated to neutrality without significant formationof apatite or other unavailable phosphate. My present invention,described infra, constitutes a practical and economical method by whichthis may be accomplished.

Various materials have been suggested in the prior art for addition tonitric acid-rock extracts in relatively small proportions to permitammoniation of the extract to neutrality without degradation of thephosphate to unavailable forms. Among the materials suggested have beensulfuric acid (in proportion less than that required to adjust CaO:P Omole ratio to 2), potassium sulfate, and compounds of magnesium,aluminum, and other metals. I have tested the suggested additives andhave found them to be ineffective when used in economical proportions.While one of these materials, namely, sulfuric acid, did increase theneutral citrate solubility of the precipitated phosphate in my tests,the alkaline citrate solubility which often is more closely related toagronomic response was not increased by use of sulfuric acid. X-rayanalyses of the products made with sulfuric acid additive showed thatthe formation of apatite had not been prevented by the use of sulfuricacid. The apatite that formed in the presence of sulfate was however ofreduced particle size, which explains the relatively high solubility ofthe P 0 in neutral citrate reagent. Such indicated high solubility,therefore, constitutes a false indication of agronomic value of the P 0content of such a suspension.

I have found that the addition of a relatively small amount of materialsselected from a group which is believed to act as a reaction inhibitorsuch, for example, as soluble acyclic polyphosphate compounds, topartially ammoniated nitric acid-phosphate rock extract is highlyeffective in preventing formation of apatite and other unavailablecompounds during the subsequent ammoniation to neutrality.

I have found that the resultant neutralized extract containsprecipitated phosphate almost exclusively in the form of dicalciumphosphate; hence, both neutral and alkaline citrate solubilities thereofare high. Although the solution phase of the so neutralized extractcontains considerable amounts of soluble calcium, I have found that theadded reaction inhibiting material effectively acts in a manner to forma protective coating on or otherwise inactivate the surface of thedicalcium phosphate particles to inhibit their reaction with the solublecalcium to form apatite. I am therefore able to handle nitric acidextracts of phosphate rock such as, for example, the ammoniationthereof, in a manner so as to inhibit the undesirable formation ofapatite and other phosphate compounds that are unavailable as nutrientsto growing plants and, in fact, I have found that through the use of myreaction inhibiting materials the ammoniation of such extracts toneutrality results in precipitation of the P 0 almost exclusively asdicalcium phosphate, a compound which is generally recognized as ahighly effective source of phosphorus for the growing plant.

It is therefore an object of the present invention to provide animproved method of handling nitric acidphosphate rock extracts toimprove the ammoniation characteristics thereof in a manner so as toprevent the formation of apatite and other unavailable compounds whensuch nitric acid-phosphate rock extracts are subsequently ammoniated toneutrality.

Still another object of the present invention is to provide an improvedmethod of handling nitric acidphosphate rock extracts to improve theammoniation characteristics thereof in a manner so as to prevent theformation of apatite and other unavailable compounds when such nitricacid-phosphate rock extracts are subsequently ammoniated to neutrality;said improved method characterized by the fact that when said nitricacidphosphate rock extracts are subsequently ammoniated to neutralitythe precipitation resulting therefrom is substantially dicalciumphosphate, a compound that is recognized as a highly effective source ofphosphorus for growing plants.

A further object of the present invention is to provide an improvedmethod of handling nitric acid-phosphate rock extracts to improve theammoniation characteristics thereof in a manner so as to prevent theformation of apatite and other unavailable compounds when such nitricacid-phosphate rock extracts are subsequently ammoniated to pH aboveabout 2.3; said improved method characterized by the fact that theacid-rock extract sensitivity to local overammoniation is substantiallyreduced, thereby greatly enhancing the economics of the process bylimiting the subsequent loss of P 0 availability during said ammoniationand by eliminating the need for expensive equipment or procedures, suchas multistage ammoniators, that are normally employed to preventlocalized overammoniation.

Still further and more general objects and advantages of the presentinvention will appear from the more detailed description set forthbelow, it being understood, however, that this more detailed descriptionis given by way of illustration and experimentation only and not by wayof limitation, since various changes therein may be made by thoseskilled in the art without departing from the true spirit and scopeunderlying the concept of the present invention.

In carrying out the objects of my invention in one form thereof, I haveemployed as my reaction inhibiting material certain polyphosphatematerials, namely, solutionsoluble acyclic polyphosphates. Bysolution-soluble acyclic polyphosphates I mean those sources of acyclicpolyphosphate materials which are soluble in the solution with which myinvention is concerned, i.e., the nitric acid-phosphate rock extractsuspension. In the broadest embodiments of my invention, my discoveriesdictate that the source material to be used as my reaction inhibitorneed only be such a material which, when in solution, is able to furnishthe necessary acyclic polyphosphate anions. In certain preferredembodiments I have used as a source for such acyclic polyphosphateammoniated superphosphoric acids. Although superphosphoric acidhydrolyzes very quickly to orthophosphoric acid at slightly elevatedtemperature when mixed with water, it is possible to ammoniate thesuperphosphoric acid substantially to the neutral point without anyappreciable hydrolysis. The resulting solution of ammonium salts ofacyclic polyphosphoric acids is stable, as is shown in US. LettersPatent No. 2,950,961, Striplin et al., assigned to the assignee of thepresent invention. In other embodiments of my invention I have usedother sources for the solution-soluble acyclic polyphosphates andmixtures thereof. Among these are (l) alkaline earth polyphosphates, forexample, calcium and magnesium polyphosphates; (2) alkali polyphosphatesincluding, for example, ammonium, sodium, and potas sium polyphosphates;and (3) superphosphoric acid and derivatives thereof, one of whichderivatives has been shown in my preferred embodiment supra to beammoniated superphosphoric acids which also is included in the alkalipolyphosphate (2) above.

In one test typical of those using metallic salts as the reactioninhibitor, essentially pure sodium tripolyphosphate was used as thereaction inhibitor material. In this test, phosphate rock was extractedwith nitric acid in the usual manner and the extract was ammoniated topH 2.3 prior to addition of the sodium tripolyphosphate. The sodiumtripolyphosphate, in pulverant form, was then added in proportionsufficient to provide 15 percent of the total P in the final productsand ammoniation to neutrality was completed. Results were in every wayequal to those obtained with the ammoniated superphosphoric acid (1 1-37-0) which I prefer to use as a source of polyphosphate because of itsready availability on the fertilizer market and its relatively low cost.With the sodium tripolyphosphate inhibitor, both neutral and alkalinecitrate solubilities of P 0 in the neutral product exceeded 90 percent,which result provides a demonstration of the effectiveness of solublemetallic polyphosphates, which I include among those materials that Ifind to be effective reaction inhibitors.

In another series of tests, the polyphosphate additive (11-37-0ammoniated superphosphoric acid) was highly effective even when added insuch a small proportion that only percent of the total phosphate in thefinal suspension was derived from the additive; the proportion of P 0added as polyphosphate in this case represented only about 7 percent ofthe total phosphate. Addition of this proportion of polyphosphate (test51) effected an increase in neutral citrate solubility of the P 0 fromabout 75 to 95 percent and an increase in alkaline citrate solubilityfrom only 30 percent to 79 percent. Even greater increases in neutralcitrate solubility and alkaline citrate solubility were effected byusing slightly higher proportion of polyphosphate. For example, when 15percent of the total P 0 was derived from 11-37-0 (about 10 percent ofthe total P 0 as polyphosphate [test 45]), neutral citrate solubility ofthe P 0 was 98 percent and alkaline citrate solubility was 91 percent.Use of higher proportions of 11-37-0, such as 20 percent: of the total P0 (test 46) and 30 percent of the total P 0 (test 47) similarly resultedin high neutral and alkaline citrate solubilities.

Petrographic examination of the solid phases of the neutralizedsuspensions showed that when polyphosphate additive was used the majorphosphate present was anhydrous dicalcium phosphate, whereas withoutpolyphosphate the major solid was apatite. Chemical analyses showed thatwhen polyphosphate additive was used about 20 percent of the calciumremained in the solution phase, thus offering evidence of theeffectiveness of the polyphosphate in inhibiting reaction betweensoluble calcium and the solid dicalcium phosphate in the suspension.Without additive, only 5 percent of the calcium was found in thesolution phase.

Both the products made with 10 percent of the P 0 from ll37-0 (test 51)and those made with 15 percent from 11-37-0 (test 45) evidenced someslight reversion to apatite during storage after about 45 days. Thus,these amounts of polyphosphates (7 and 10 percent respectively) for asuspension that is to be utilized immediately are quite sufficient;however, these amounts probably would not be completely sulficient for asuspension which was intended to be held in long-term storage (more thanabout 2 months). However, product made with 20 percent of the P 0 froml137-0 (14 percent of the P 0 from polyphosphate) was unchanged (highlysoluble) after 45 days of storage at room temperature and that made with30 percent of the P 0 from 11-37-0 was essentially unchanged after 75days of storage.

I have also discovered in this series of tests that there is an optimumpH range in which to add the 11-37-0 during the ammoniation step. Forexample, ammoniation of the acid-rock extract was carried to differentdegrees of completion, as indicated by pH measurements, prior toaddition of the l1-37-0. Immediately after addition of the 11-370,ammoniation was resumed and carried to, or slightly above, neutral pH.The results showed that addition of 11-37- 0 was most effective ininhibiting apatite formation and increasing neutral and alkaline citratesolubilities when it was added to extract that had been ammoniated atleast to pH 1.9 and to no higher than about pH 2.5. When addition wasmade below this pH range, the 1l-37-0 was ineffective, probably becauseits polyphosphate constituent was rapidly hydrolyzed at the low pH. Whenaddition was made above the optimum range, effectiveness of the 11-37-0was reduced because significant amounts of apatite had formed prior tothe addition.

Aside from the advantages already pointed out for use of 11370 or otherpolyphosphate additive in the ammoniation of nitric acid-rock extract,there is at least one other advantage; namely, the reduction insensitivity of the extract to localized overammoniation. In existingnitric phosphate processes, considerable precautions and accompanyingextra expense are involved in preventing localized overammoniation andsubsequent loss of P 0 availability in the ammoniation systems. Typicalprecautions are the provision of multistage ammoniators and thelimitation of ammoniation rates to low values. However, with addition ofpolyphosphates to inhibit formation of unavailable P 0 duringammoniation, according to my invention, it should be possible to largelydispense with these precautions and thereby effect savings in equipmentand operating costs.

My invention together with further objects and advantages thereof willbe better understood from a consideration of the following descriptions,examples, and tabulations, taken in connection with the accompanyingdrawings in which:

FIGURE 1 is a diagrammatical illustration of the effect of one of myreaction-inhibiting materials on availability of P in neutral nitricphosphate slurries. It confirms that there is in fact a favorable eifectof addition of one of my reaction-inhibiting materials on neutralammonium citrate solubility, and further, that there is a favorableeffect on alkaline citrate solubility of the P 0 FIGURE 2 is adiagrammatical illustration of the effect that one of myreaction-inhibiting materials has on the solubility of P 0 in nitricphosphate slurries at various pH levels.

FIGURE 3 is a diagrammatical illustration of the marked decrease in bothneutral citrate and alkaline citrate solubility when unadjusted nitricacid-phosphate rock extracts are subjected to ammoniation without thebenefit of an additive from the group of materials C0mprising myreaction-inhibiting materials. Also shown is the marked decrease in thedicalcium phosphate constituent in such unadjusted extracts whensubjected to ammoniation.

FIGURE 4 is a diagrammatical illustration of the marked decrease in bothneutral citrate and alkaline citrate solubility when nitricacid-phosphate rock extracts, blended with sources of potassium andphosphoric acid to yield a slurry of 1: 1:1 ratio, are subjected toammoniation without the benefit of an additive from the group ofmaterials comprising my reaction-inhibiting materials. Also shown is themarked decrease in the dicalcium phosphate constituent in suchunadjusted extracts when subjected to subsequent ammoniation.

FIGURE 5 is a diagrammatical illustration intended for direct comparisonwith FIGURE 4 supra. In the case of FIGURE 5, the nitric phosphateslurry of a 1:1:1 ratio was prepared by my recommended procedure whichinvolves introduction of an additive selected from the group comprisingmy reaction inhibitor materials prior to ammoniation thereof.

FIGURE 6 is a diagrammatical illustration of the lack of desired effectthat various sulfate additives have on maintaining high degrees of P 0solubility during ammoniation of nitric phosphate suspensions, and moreparticularly, that such sulfate additives are ineffective in maintaininghigh neutral citrate solubility when the addition is withheld untilafter ammoniation is carried to above a pH of about 2.5, and still moreparticularly that as to alkaline citrate solubility, said sulfateadditives resulted in only a very small increase over that obtainedwithout the benefit of any additive regardless of the pH at which saidadditive was incorporated during the ammoniation thereof.

FIGURE 7 is a diagrammatical illustration of further refinements of testdata plotted in FIGURE 6 supra and clearly shows that the presence ofthe sulfate additive did not prevent formation of apatite.

FIGURE 8 is a diagrammatical illustration of the results of growth testsof corn plants carried out in a greenhouse. In this figure, a relativeyield of 100 percent represents the dry weight of corn plants after 6weeks growth in a pot of soil fertilized with nitric phosphatesuspension prepared with introduction of an additive selected from thegroup comprising my reaction inhibitor materials prior to ammoniationthereof. It is readily seen from this figure that the growth was about40 percent less in a pot treated in exactly the same manner exceptfertilized with a nitric phosphate suspension prepared without thebenefit of an additive from the group comprising my reaction inhibitormaterials.

In order that those skilled in the art may better understand how thepresent invention can be practiced and more fully and definitelyunderstood, the following examples of my processes which I have used inimproving the method of handling nitric acid-phosphate rock extracts toimprove the ammoniation characteristics thereof, as has been indicatedherein, are given by way of illustration and not by way of limitation.

8 EXAMPLE I-FIGURE 1 Reference is now made more specifically toFIGURE 1. A series of exploratory tests had indicated that addition ofammonium polyphosphate (11-37-0 liquid fertilizer) to nitric phosphatesuspension during ammoniation might permit ammoniation to neutralitywithout serious loss of neutral citrate availability. When 11 370equivalent to 10 percent of the total P 0 was added during ammoniation(added at pH 2.4) and ammoniation was continued to pH of about 8, theneutral citrate solubility of the P 0 was 97 percent; the alkalinecitrate solubility of the P 0 was not determined. The further tests,results of which are represented by FIGURE 1, confirm the favorableeffect of addition of ll370 on neutral ammonium citrate solubility and,further, show a favorable effect on alkaline citrate solubility of the P0 Results of these tests are given in Table I below and also inFIGURE 1. As will be discussed, P 0 solubilities decreased duringlong-term storage (30-40 days) except when at least 20 percent of thetotal P 0 was from 11-37-0.

The materials used in the tests were Florida flotation concentrate 10mesh), 42 percent nitric acid, anhydrous gaseous ammonia, and 11-37-0grade ammoniated superphosphoric acid. Extraction and ammoniation werecarried out in the same vessel (cylindrical jar, 8% inches in diameterand 9% inches high). Two 2-inch air-driven propellers were used foragitation. They were positioned about 1 inch above the bottom the vesseland about degrees apart. Ammonia was metered with a rotameter and fed at12.9 grams per minute through a ring sparger located near the bottom ofthe vessel. The sparger was a 5-inch ring of A-inch tubing thatcontained 20 uniformly spaced, /gg-ll'lch ports facing toward thebottom.

In making a test, phosphate rock was added to the preparation vessel(about 2 minutes) containing the nitric acid. An antifoarning agent (20to 30 drops) was used as necessary to control foaming. After the rockwas added (1200 g. phosphate rock/batch, 20 minutes was allowed forextraction. In all tests, sufficient nitric acid was used to give an HNO:CaO mole ratio of 1.86, which was established in earlier work as aboutthe minimum acidzlime ratio for complete dissolution of rock P 0 inabout 20 minutes. Ammoniation was begun immediately after the 20-minuteextraction period. In tests in which 1137-0 was added, ammoniation wasinterrupted at pH of 2.3 to 2.9 and the 11-370 was poured rapidly intothe suspension. Previous tests had indicated that precipitation ofunavailable P 0 had not yet begun at pH of about 2.4. It was consideredinadvisable to add the 11-37-0 at lower pH because of increasedpossibility of hydrolysis of the polyphosphate at low pH. After additionof l1-37-0, ammoniation was resumed and carried to pH of 7.5 to 8.5.

The results of these tests show that addition of as little as 15 percentof the total P 0 as 11-37-0 (test 45) permitted production of neutralsuspension with 98 percent P 0 solubility in neutral citrate and 91percent solubility in alkaline citrate. In a comparable test with noadditive (test 49), P 0 solubility was only 78 percent in neutralcitrate and 30 percent in alkaline citrate. The 78 percent solubility ofthe product with no additive, although higher than would be expectedfrom some previous data on production of solid nitric phosphates (TVAreprint 157J. Agr. Food Chem. 1 67277, 1953), is in agreement with datafrom a previous test in which a similar suspension was prepared. Thegrade of the suspension made with 15 percent of the P 0 furnished as11370 was 11.6- 11.10. Physical properties of the suspension were good.After standing for 1 day, no settling was evident. Viscosity was only128 centipoises and 99 percent was pourable in a standard pour test. ThepH of the suspension was 8.5 immediately after preparation and wasessentially unchanged after 7 days. However, after 46 days of standing,the pH had dropped to 4.6, and the P 0 solubility had 1 Nielsson, It..l., Yates, L, D., J. Agr. Food Chem. 1 672-77 (1953).

9 dropped to 72 percent by the A.O.A.C. method and 51 percent by thealkaline citrate method.

For comparison purposes, two tests were made (data not shown) in which15 percent of the total P in suspension was furnished as orthophosphoricacid in exactly the same manner as 11-37-() was used in test 45. Allconditions, including degree of ammoniation, were essentially the sameas those in the test with 11-37-0. The results indicated no benefit fromaddition of the orthophosphoric (2.9-6.5) at which these proportions of11-37-0 were added. The water solubility of the P 0 in the slurries wasnot increased by use of 11-37-0; solubility was less than percent inmost tests. This indicated that the favorable effects of 113 7-0 onneutral and alkaline citrate solubility are due to formation of solidphosphate that is soluble in these reagents but insoluble in water.Petrographic examination showed the presence of substantially onlydicalcium phosphate.

TABLE I.EFFEGT OF 11-37-0 ADDITIVE ON PROPERTIES OF NEUTRAL NITRICPHOSPHATE SUSPENSIONS Test Number 49 44 51 45 46 47 Additive None11-37-0 ammoniated superphosphorie acid P105 from additive, percent oftotal P105 0 10 10 Formulation, lb./ton of product:

Phosphate rock a 629 620 594 606 578 555 Nitric acid (42% HNO3) l, 4631, 441 1, 380 1, 410 1, 343 1, 290 Additive, 11-37-0 liquid fertilizer 061 59 95 129 211 Ammonia (gaseous, anhydrous)... 163 127 134 140 130 131Extraction:

HNOnCaO mole ratio 1. 86 1. 86 1. 86 1. 86 1. 86 1. 86 Time, min 20 2020 2d 20 20 Ammoniation:

H at which 11370 was added 2. 7 2. 4 2. 9 2. 5 2. 9 erminal pH 7. 5 7.98.4 8. 5 8. 5 8.0 pH after 3-7 days 4. 6 3.1 8.2 8. 4 8.4 8. 1 NHaINOamole ratio (by analysis 0.87 0.85 0.81 0. 85 0. 90 l]. 98 C210 :PzOsmole ratio (after ad 11 of additive) 3. 66 3. 24 3. 24 3. 05 2. 87 2. 52Chemical analysis of slurry, percent:

TotalN 12.7 12.2 11.2 11.6 11.4 11.6 NH N 5. 9 5. 6 5. 0 5. 3 5. 4 5. 7Total P205 10. 2 11. 1 10. 7 11. 3 11.5 12. 6 Neutral citrate-solubleP105 8.0 9.1 10. 2 11. 1 11. 2 12. 1 Alkaline citrate-soluble PaOs 3. 14. 8 8. 5 10. 3 10.8 11. 3 Water-soluble P20 0. 4 1.0 0. 1 0.2 1. 0 1. 2P 05 solubility, percent of total P205:

Neutral citrate (A.O.A.C.) I 78 82 95 98 97 96 Alkaline citrate s 30 4379 91 94 90 Water soluble 4 9 1 2 9 10 Physical properties oi slurry(after standing 1 day at 7580 F.):

Apparent viscosity, eentipoises.. 96 176 430 128: 132 196 Settled,percent 2 3 0 t1 4 5 Pourabrlityn percent 99 97 98 99 95 96 2 Includeswater-soluble P10 5 11 Brookfield viscometer at 100 r.p.m. i Clearlayer, percent of total volume. 1 Percent pourahle in 1 minute fromquart jar tilted degrees.

acid; neutral citrate solubility was only to percent and alkalinecitrate solubility was only about 23 percent. The slightly lower neutralcitrate solubility in these tests, as compared with that in the testswithout additive was probably due to slightly low degree of ammoniationin the tests without additive.

Use of ll-37-0 additive in the proportion of only 10 percent of thetotal P 0 (tests 44 and 51) instead of 15 percent gave fairly highsolubilities (95 percent neutral citrate; 79 percent alkaline citrate)when the addition was made at pH 2.4 (test 51). However, solubilitieswere considerably lower (82 percent neutral citrate; 43 percent alkalinecitrate) when addition of the 10 percent proportion of 11-37-() was madeat pH 2.7 (test 44). This result suggested that the pH at the time ofaddition of 11-374) is critical and subsequent tests, which will bedescribed in detail, established the pH range of 1.9 to 2.5 as theoptimum for addition of the reaction inhibitor material. The productmade with 10 percent of the P 0 from 1l37-0 (added at pH 2.4; test 51)showed drop in pH and loss of P 0 solubility during long-term storage.After 36 days, the pH was 3.5, A.O.A.C. solubility was 76 percent, andalkaline citrate solubility was 61 percent.

Use of 11-37-0 equivalent to 20 percent of the total P 0 (test 46) gavevery high solubilities (97 percent neutral citrate; 94 percent alkalinecitrate). Grade of this product was 11.4-11.2-0 and physical propertieswere good. There was no drop in pH or significant loss in P 0 solubilityduring 44 days of storage. Slightly lower P 0 solubilities were obtainedin tests in which 30 and 40 percent of the P 0 was furnished as 11-37-0;however, this apparently was a result of inadvertently high pH EXAMPLE1IFIGURE 2 Efiect of pH at time of addition A IZOD-gram charge of minus10-mesh Florida flotation concentrate was extracted batchwise with 42percent nitric acid; the HNO :CaO extraction mole ratio was 1.86. Aftera 20 minute extraction period, batchwise ammoniation with gaseousanhydrous ammonia was begun in the extraction vessel. When a specifieddegree of ammoniation had been reached, as indicated by measurement ofpH of the slurry, ammoniation was stopped momentarily and 11-37-0ammoniated superphosphoric acid, equivalent to 15 percent of the total P0 in the final suspension, was added. Ammoniation then was resumed andcarried to about pH 8. In a series of seven tests (Table II below andFIGURE 2), the pH at which the 11-37-41 was added was varied from 1 to4.1 to determine the effect of this variable. Portions of the resultantslurries were analyzed within 1 week while other portions were used todetermine handling and storage properties including effects of storageon P 0 solubility. For comparison purposes, one test (No. 63, Table II)was made without any additive, another (No. 55) with orthophosphoricacid as the additive, and a third (No. 66) with ammoniatedorthophosphoric acid (8-240 grade).

Results in this series of tests show that the highest neutral andalkaline citrate solubilities of P 0 were obtained when the 11-37-0 wasadded in the pH range of about 1.9 to 2.5 (tests 58, 45, and 57). Withaddition in this range, neutral citrate solubility was above 95 percentand alkaline citrate solubility was above percent 1 1 as compared with67 and 25 percent, respectively, when 11-37-0 was omitted (test 63,Table II).

When 11-370 was added before the optimum pH range was reached, thealkaline citrate solubility was drastically reduced and the neutralcitrate solubility was reduced somewhat also. For example, when additionwas at pH 1.7 (test 56), the neutral and alkaline citrate solubilitieswere only 93 and 80 percent, respectively. When the 11370 was addedbefore ammoniation was started (pH 1; test 62), the respectiveavailabilities were only 86 and 51 percent.

Withholding addition of the 1137-0 until after the optimum pH range hadbeen exceeded (for example, addition at pH 3.1 and 4.1 in tests 61 and60, respectively) likewise gave reduced neutral and alkaline citratesolubilities. Apparently some insoluble apatite had formed prior toaddition of the 11-37-0 and persisted after the addition of 1137-0.

Neither orthophosphoric acid additive (test 55) nor 8-240 ammoniatedorthophosphoric acid (test 66) were effective in increasing neutral oralkaline citrate solubility of P in slurries. Although these materialswere added in the same proportion (15 percent of total P 0 as was the11-37-0, the neutral and alkaline citrate solubilities of the P 0 wereessentially the same as without any additive (test 63). This constitutesstrong evidence that the polyphosphate content of the 11-37() is theeffective agent in increasing P 0 solubilities.

version of P 0 to apatite or other unavailable forms of phosphate,special chemical analyses and petrographic examinations were made in onetest (similar to test 45, Table II) in which 11-37-0 was added (15percent of total P 0 at pH 2.3 and in another test (test 66, Table II)111 WhlCl'l the same amount of 8-24-0 ammonrated orthophosphoric acidwas added at the same pH. The special analyses included total CaO,water-soluble CaO, and water-soluble nitrogen. Results of the chemicalanalyses, which were made within 1 week of preparation of thesuspensions, are summarized in the following tabulation:

Test with Poly- Orthophosphate phosphate (1137-0) (8-24-0) additiveadditive Percent of total CaO:

In solids 79 95 In liquid. 21 5 CaO;P O mole re 10 in so 1 s 2.5 3.2Percent of total nitrogen:

In solids 1 0 In liquid 99 100 These results show that with 11-37-0additive 21 per- 25 cent of the total calcium was held in the solutionphase during ammoniation as compared with only 5 percent whenpolyphosphate was not used. As a result, the CaO: P 0 mole ratio in thesolid phase of the slurry with TABLE II.-EFFECT OF PHOSPHATE ADDI'IIVESIN BATCH AMMONIATION OF NITRIC PHOSPHATE SUSPENSION FERTILIZERS TestNumber 63 62 56 58 57 61 55 66 8-24-0 am- Orthophosmonlated phoric acidorthophos- Type of additive B None 11-37-0 ammoniated superpliosphoricacid b H3PO phorie acid pH at time of addition 1 0 1.7 1. 9 2. 3 2. 5 3.1 4.1 2. 3 2. 3

P 0 from additive, percent of total P105 0 15 15 15 15 15 15 15 15 15Formulation, lb./ton of P205 in product:

Phosphate rock 6,060 5, 160 5,160 5, 160 5, 160 5,160 5,160 5, 160 5,160 5, 160 Nitric acid (42% HNO 14, 340 12, 200 12, 200 12, 200 12, 20012, 200 12, 200 12,200 12,200 12, 200 Additive:

11-37-0 811 811 811 811 811 811 811 Orthophosphoric acid (80% H PO4) 5188-24-0 ammoniated H3P04 1, 250 Ammonia (gaseous anhydrous) 1, 590 1, 6021,197 1,184 1,002 1,241 1,226 1,366 1, 511 1,410 Water g 0 1, 510 863641 213 430 0 0 0 Extraction:

HNO =CaO mole ratio 1. 86 1. 86 1. 86 1. 86 1. 86 1. 86 1. 86 1. 86 1.86 1. 86 Time, min 20 20 20 2O 20 20 20 20 2O 20 Anunoniation:

HQIHNOQ mole ratio (by analysis) 0. 94 1. 15 0.93 0.95 0.85 0.97 0. 941.05 1. 09 1 11 CaOzPzOs mole ratio (afteiaddition of additive). 3. 643. 05 3. 05 3. 05 3.05 3. 05 3. 05 3. 05 3.05 3. 05 pH at end ofammoniation 8. 2 8. 5 8.3 8.4 8. 5 8. 5 8. 5 8. 5 8. 2 8. 3 pH after 6days 8. 3 8.8 8. 6 8. 6 8. 4 8.8 8. 7 8.7 8. 7 Chemical analysis ofslurry, percent:

Total N 13.5 12. 8 11. 8 l1. 9 11. 6 12. 2 12.5 13. 3 14. 2 13. 2 6.66.9 5.7 5.8 5.3 6.0 6.1 6.8 7.4 7.0 O 10.1 9.8 10.6 10.9 11.3 10.8 11.111.2 11.9 11.1 Neutral citrate-soluble P205 1 6. 8 8. 4 9. 9 10. 5 11. 110. 5 10. 0 9. 2 7. 3 7 1 Alkaline citrate-soluble P205 i 2. 5 5. 0 8. 510. 1 10.3 9. 8 8. 3 6. 9 2. 7 2. 6 Water-soluble P205 0.1 1.9 0.9 1. 30.2 1. 2 1. 1 2.1 0. 6 1, 0 P205 solubility, percent of total P20Neutral citrate (11.0 .A.C.) 67 86 93 06 98 97 82 61 64 Alkaline citratei 25 51 80 93 J1 91 75 62 23 23 Water soluble 1 19 9 12 2 11 10 19 5 9Physical properties after 1 day at 75 Apparent viseosity, centipoises 4856 112 212 128 120 120 112 52 4 0 Settled} percent 3 8 6 0 0 3 0 0 26 3699 99 99 98 99 99 99 98 98 98 Pourability, percen a Added duringammoniation, at pH indicated.

b 11.1% N; 37.0% P 0 (71% of P205 in nonortho iorrn).

11370 added before start of ammoniation.

d Remainder of P20 was from rock.

a Florida flotation concentrate; -10 mesh, 33.0% P10 47.5% CaO. fQuantities calculated from NH zPgo ratio in final slurry.

Mechanism of action: To provide information as to the mechanism by which11370 additive inhibits re- 1; Water was added as required to maintainfluidity.

h Analyses made within 1 week of preparation.

i Includes water-soluble P20 1 Brookfield viscometer at 100 r.p.m.

11 Clear layer, percent of total volume.

1 Percent pourable in 1 minute from quart jar tilted 45 degrees.

11-37-0 additive was only 2.5, which indicates a high content ofdicalcium phosphate (CaO:P O mole ratio:

2.0). Petrographic examination confirmed that the solids P was from11-37-0, there was no significant change in this test were largelyanhydrous dicalcium phosphate in solubility or pH in this length oftime. Further pH with apatite present only as a minor phase. In the testmeasurements and P 0 solubility determinations were withoutpolyphosphate additive, 95 percent of the total made after 60 to 75 daysof storage. These measurements, CaO was found in the solid phase. TheCaO:P O mole together with the previously mentioned ones, are sumratio(3.2) in this solid corresponded closely to that of 5 marized in TableIII below.

TABLE IIL-EFFECT OF STORAGE ON pH AND P20 SOLUBILITY OF NITRIC PHOSPHATESUSPENSION FERTILIZERS MADE WITH 11-37-0 ADDITIVE Test Number 51 45 4647 P20 from 11-37-0, percent of total P 0 b 30 Days of storage (75-80F.) 7 36 7 46 60 7 44 60 7 75 pH P 0 solubility, percent of total P20Neutral citrate (A.O.A.O.) l. Alkaline citrate (Netherlands method)Water soluble a Data on preparation given in Example I. b 11-37-0 addedto partially ammoniated slurry of pH 2.3 to 2.9; ammoniation thencarried to pH 8.0-8.5.

apatite, and petrographic examination confirmed that Data in Table IIIsupra show that the suspension made apatite was the major constituent.Dicalcium phosphate with 20 percent of the P 0 from 11-37-0, althougheswas present only in a very minor proportion. In the tests sentiallyunaffected by 44 days of storage, deteriorated both with and without11-37-0 additive, essentially all significantly between the forty-fourthand sixtieth day of of the nitrogen was in the solution phase of theslurry, storage. Neutral citrate solubility dropped from 97 per- Whichdiscounts the Possibility that the 11-374) might cent to 87 percent,alkaline citrate solubility dropped from be promoting formation ofcalcium ammonium phosphate 91 percent to 63 percent, and pH dropped from8.2 to 5.1. compounds insoluble in the suspension. The product made with30 percent of the P 0 from In another series of tests, a blend of reagen-grade 11-37-0, however, did not lose significant P 0 solubilitydicalcium phosphate, calcium oxide, and calcium fluoride in 75 days fstorage and pH ain d hi h (7,6 vs. was substituted for phosphate rock inthe preparation of i iti l 81)), nitric phosphate Suspension with and utuse of The data show also that the product made with only 15 1137()additive. Chemical and petrographic studies in percent of the P 0 from11-37-0, which lost considerthis series showed the same eifects of11-37() as were able solubility during 46 days of storage, deterioratedfurdescribed above for the tests with phosphate rock. These ther duringstorage for 60 days. After 60 days, the neutral tests demonstrated,therefore, that the effects of 11-37-0 4Q citrate solubility was only 66percent, the alkaline citrate are independent of the iron, aluminum, orother impurity solubility was only 47 percent, and pH had dropped tocontent of the rock. 3.3 from an initial 8.5.

In still another series of tests it was determined that in There was noconsistent efiect of storage on water neutral suspension prepared withpolyphosphate additive solubility of P 0 which ranged from 1 to 11percent. according to my recommended procedures, the polyphos- Therewas, however, a clear relationship between pH of phate is associatedintimately with the solid phase of the the slurry and P 0 citratesolubilities. Decreases in P 0 suspension, most probably as a protectivecoating on the solubility were in all cases accompanied by significantsurface of dicalcium phosphate crystals, which inhibits drops in pH. Itis assumed that the deterioration of the reaction of the dicalciumphosphate with soluble calcium slurries during storage is a result ofslow hydrolysis of the in the solution phase of the suspension. Analysesfailed polyphosphate. In the absence of polyphosphate inhibitor, todetect any polyphosphate in the solution phase of the calcium nitrate inthe solution phase apparently reacted final neutral suspension.Furthermore, it was determined with the precipitated dicalcium phosphateto form apatite that the inhibited solid phase was unreactive towardgenerally in accordance with the following equation: soluble calcium,whereas, soluble calcium in the solution phase was highly reactivetoward fresh, uninhibited dis)2+ '4+ m z(P04)6+ O3 calcium phosphatecrystals added to the liquid phase. The accompanying formation of nitricacid is apparently From the results of these various series of tests, Ihave responsible for the observed drop in pH. concluded that additivesfrom the group of materials com- EXAMPLE 1V FIGURES 3 AND 4 prising myreaction inhibitor materials function through interaction of theadditive with solid dicalcium phosphate Tests without acyclicpolyphosphate additive-Negative in suspensions to coat or otherwiseprotect this dicalcium examples hosphate from reaction with solublecalcium resent in the solution phase. Thereby, reversion of the ilicalcium Referring now more: speclficauy 9 F U a test phosphate toapatite or other unavailable forms of phos- (test 92) was made m wlilcha .extract of phate is prevented. phosphate rock was ammoniatecl withoutadditives of any kind including materials comprising my reaction 1nh1b1-EXAMPLE III tors. In this test, the proportion of nitric acid (42 per-Smrage tests cent HNO concentration) used in the extraction stepprovided a HNO :CaO mole ratio of 1.86 which, as has In precedingexamples, data on pH and P 0 solubility been indicated supra, was foundto be about the minimum were given for suspensions of various 11-37-0contents required for complete solubilization of P 0 in the rock. thathad been stored 36 to 46 days at to F. In The CaO:P O mole ratio in theextract was 3.64, the that length of storage, there was considerableloss of P 0 same as that in the rock from which the extract wasprecitrate solubility and drop in pH when the suspensions pared. Theconditions under which this test was conwere made with 10 or 15 percentof the P 0 furnished ducted and results therefrom are shown in Table IVas 11-37-0. However, when about 20 percent of the 75 below and in FIGURE3.

TABLE IV.PREPARATION OF NITRIC PHOSPHATE SUSPENSIONS BY BATCHAMMONIATION OF ROCK-ACID EXTRACT WITH AND WITHOUT POLYPHOSPHATE ADDITIVETest Number 92 99 100 Test with Tests without poly- 11-37-0 phosphateadditive additive Unadjusted Nominal grade extract 9-9-9 9-9-9 P105 fromrock, percent of total P205 100 80 85 Formulation, lb./ton of P105 inproduct:

Phosphate rock 6, 060 4, 848 5, 152 Nitric acid (42% HN O3) 14, 340 12,704 13, 500 Additives:

ll37--0 O 811 Orthophosphoric acid (54% P205) 0 741 0 Potassium chloride(62% K) 0 3, 236 3, 220 Ammonia (gaseous anhydrous) 1, 526 1, 510 1,34.9 Extraction:

HNOs:Ca.O mole ratio 1. 86 2. 06 2.06 (HNO3+U.5 H PO4);GaO mole ratio2.13 Time, min 20 20 Ammoniation:

CaO2P205 mole ratio (after addition of additive if an 3. 64 2. 91 3.10Final NHazHNOa mole ratio- 0. 94 1.05 0. 88 pH at end of ammoniation...8. 0 8.2 8. 2 pH after 1 day 8.4 7. 0 8. 3 Chemical analysis of finalslurry is perce Total N l2. 8 12.1 10. 5 NHaN--. 6.2 6. 2 4. 9 TotalP205. 10. 4 9. 9 9. 6 Neutral citrate-soluble P105 8. 3 8.0 9. 7Alkaline citrate-soluble P 0 3. 5 5. 3 8. 5 P 05 solubility, percent oftotal P20 Neutral citrate (A.O.A.C.) h 79. 8 80. 8 100 Alkaline citrate11 33. 7 53. 5 88. 5

b Remainder from additive.

0 Florida flotation concentrate; 33.0% P 0 47.5% 0210. Size --10 mesh.

d Wet-process caid; acid added to HNOa prior to extraction. 9 Quantityaciculated from NHaZNOJ ratio in final slurr y 1 Effective acidulationratio, based on assumption that H3PO reacts with rock to formmonocalcium phosphate.

8 Chemical analyses made 1 day after preparation of slurry. 11 Includeswater-soluble P205.

Sampling during ammoniation covered the range of ammoniation from about0.5 to 1.0 NH :NO mole ratio, which corresponded to a pH range of about2 to 8.3. An N:P O weight ratio of 1:1 in the slurry was reached withammoniation to only about 0.5 NH :NO mole ratio. With this degree ofammoniation, both neutral and alkaline citrate solubility of the P 0were essentially 100 percent and X-ray analyses showed that the P 0 inthe solid phase was present chiefly as dicalcium phosphate; no apatitewas present. However, with only this degree of ammoniation the slurrywas extremely acidic (pI-I 2).

Analyses of samples taken during further ammoniation of the unadjustedextract (FIGURE 3) show that formation of apatite in the slurry began atNH :NO ratio of about 0.55 (pH about 2) and progressed throughoutfurther ammoniation. This formation of apatite presumably represents aconversion of dicalcium phosphate according to the following reaction:

After ammoniation had been carried to NH :NO mole ratio of 0.8 (pH about4), only about percent of the total P 0 remained in nonapatite forms.About 10 percent of the P 0 remained as dicalcium phosphate, while theremainder of the nonapatite P 0 was accounted for largely as iron andaluminum phosphates. With further ammoniation to NH zNO mole ratio ofabout 0.95 (pH about 8), conversion of dicalcium phosphate to apatitewas essentially complete; only a trace of dicalcium phosphate was foundin the product. Other nonapatite P 0 in the product still representedabout 15 percent of the total P 0 The formation of apatite duringammoniation in this test was accompanied by decreases in solubility ofthe P 0 in both neutral and alkaline citrate reagents. With ammoniationup to NH :NO mole ratio of about 0.75 (pH about 3.5), the decreases inalkaline citrate solubility of the P 0 in the slurries corresponded veryclosely to decreases in the proportion of nonapatite as determined byX-ray analyses (FIGURE 3). Alkaline citrate solubility of P 0 in theslurry with NH :NO mole ratio of 0.75 was about 40 percent. Furtherammoniation resulted in further large decrease in the proportion ofnonapatite P 0 but did not result in a correspondingly large decrease inalkaline citrate solubility. This suggests that the apatite formed at pHabove about 3.5 probably had an appreciable solubility in the alkalinecitrate reagent, whereas, that which formed below pH 3.5 was relativelyinsoluble. Particle size studies indicated that this difference issolubility is a result, at least in part, of smaller particle size ofthe apatite formed at relatively high pH. The apatite that formed up topH 3.5 was partially insoluble also in neutral citrate reagent;formation of this apatite decreased solubility of the P 0 in neutralcitrate reagent to about percent of the total P 0 There was no furtherdecrease, however, with further ammoniation. Preliminary particle sizestudies indicated that the apatite that was insoluble in the neutralcitrate reagent was somewhat larger than that which was soluble in thisreagent.

Referring now more specifically to FIGURE 4 and to that portion of TableIV supra which relates to test 99, it is seen that neither use oforthophosphoric acid additive nor use of potassium chloride additiveprovided beneficial eifects on P 0 availability such as are obtainablethrough use of an additive selected from my group of acyclicpolyphosphate compounds. In test 99, the proportion of nitric acid usedin the extraction step provided an HNO :CaO mole ratio of 2.06. Thephosphoric acid, which was added to the nitric acid prior to extraction,provided 20 percent of the total P 0 the remainder was from the rock.Addition of this amount of phos phorie acid altered the Ca( ):P;O moleratio only from 3.64 to 2.91; thus the proportion of lime in the slurrywas still considerably in excess of that required to form only dicalciumphosphate (CaO:P O =2.0) with the P present.

Results of this test, as illustrated in FIGURE 4, show that the N:P Oratio in the product slurry reaches 1.0 at an ammoniation of 0.68 NH :NOmole ratio (pH 1.5). With this degree of ammoniation, none of the was inthe form of apatite and all was soluble in both neutral and alkalinecitrate reagents. About 55 percent of the total P 0 was found to bepresent as dicalcium phos phate. As ammoniation continued, however, theformation of apatite began and progressed until at an mole ratio of 1.0(pH 7) all but about 10 percent of the P 0 in the product was the formof apatite. These observations are based on the analytical data shown inFIGURE 4, which were obtained on l-day old samples and on X-ray dataobtained on samples several hours old. There was indication, however,from pH data that the formation of apatite was slower in this test thanin the previously described test without additive. The pH data showedthat samples ammoniated to pH above about 4 became more acidic onstanding. The phenomenon of unstable pH has been observed repeatedly inpreparation of nitric phosphate suspensions containing variousadditives. It is postulated that constituents of certain additives areto some extent absorbed by the surfaces of dicalcium phosphate crystalsin the slurry and thus interfere with reaction of the dicalciumphosphate to form apatite. Sulfuric acid additive has exhibited such ashort-term inhibiting efiect. However, as has been shown and will beshown further, the additives selected from my group of acyclicpolyphosphate compounds are superior in that their reaction inhibitingeffect is more nearly complete and of much longer duration.

EXAMPLE V--FIGURE 5 As is shown in the second portion of Example IVsupra, when a neutral slurry of 1:1:1 ratio was prepared by addingphosphoric acid and potassium chloride to nitric acid-phosphate rockextracts and subjecting the resulting slurry to ammoniation without thebenefit of an additive selected from the group comprising may reactioninhibiting materials, both the neutral citrate and alkaline citratesolubility was drastically reduced and, further, there was evidenced amarked increase of the proportion of P 0 present as apatite at theexpense of the proportion of P 0 present as dicalcium phosphate.

Referring now more specifically to FIGURE 5 and to that portion of TableIV supra which relates to test 100, it is seen that much improvedresults were obtained when suspension of 1:1:1 ratio, originallyprepared in part from nitric acid-phosphate rock extract, wassubsequently subjected to ammoniation with the benefit of an additiveselected from the group comprising my reaction inhibiting materials. Inthis test, the proportion of nitric acid used was that required to givea HNO :CaO mole ratio of 2.06 exactly as in test 99 supra. In test 100,the amount of reaction inhibiting material, specifically 11-37-0, usedwas suflicient to provide 15 percent of the total P 0 The remainder ofthe P 0 (85 percent of total) was furnished as rock. On the basis ofresults of previous tests, the 11-370 was (in this test 100) added tothe slurry after ammoniation had progressed to a pH of 2.3.

The results of this test show that the incorporation of one of myreaction inhibiting materials effectively inhibits formation of apatiteduring ammoniation to a pH of about 8. Further, both the neutral andalkaline citrate solubility of the P 0 remained about 95 percentthroughout the ammoniation. After ammoniation to pH 8, X-ray analysesindicated that less than about 5 percent of the P 0 was in the form ofapatite. Storage tests indicate that the availability of the P 0 wouldremain high under normal conditions of product handling, storage, andapplication in the field. This was based on the fact that the pH ofsamples ammoniated to various degrees remained stable for 30 days.

EXAMPLE VIFIGURES 6 AND 7 Tests with additives other than those selectedfrom the group comprising my reaction inhibiting materials Negativeexample As I have reported supra, I have tried various additives whichhave been reported in the prior art to determine if some beneficialeffects or improved ammoniation characteristics of nitric acid-phosphaterock extracts do in fact occur. As I have also indicated supra, theresults of these tests proved that what is reported along these lines inthe prior art in fact leaves much to be desired in meeting the intendedobjectives. This example therefore includes the results I have obtainedin attempting to use various of these additives and, as will be seeninfra, it is only when I use materials selected from the groupcomprising my reaction inhibiting materials wherein I am able to preventthe formation of apatite during the ammoniation of nitric acid phosphaterock extracts, slurries, or suspensions.

One series of tests was made with a relatively small proportion ofsulfate (about '60 pounds of 93 percent H or the equivalent amount ofammonium sulfate, per ton of suspension). With this proportion ofsulfate, the adjusted CaO:P O mole ratio a was 3.28, as compared with3.6 in the original rock and 2.0 in dicalcium phosphate. The solubilitydata in these tests are based on analyses made 4 to 13 days afterpreparation of suspensions.

Referring now more specifically to FIGURE 6 and to those parts of TableV that relate to tests 92, 108, 70, 80, and 94, the data illustratedtherein shows that high neutral citrate solubility of P 0 (95-100percent vs. 67-80 percent without additive) resulted when the sulfatewas added before extraction, immediately after extraction, or at anystage of ammoniation up to a pH of about 2.5. The sulfate wasineifective, however, when its addition was withheld until afterammoniation had been carriedabove pH 2.5. In this connection, it issignificant to note that pH 2.5 is about the point in the ammoniationstep at which precipitation of dicalcium phosphate is complete andconversion to apatite begins. Therefore, it appears that the sulfateadditive, in order to be effective, must be present in the system at thetime precipitation of apatite normally would begin.

Other more significant data in FIGURE 6 and Table V show that use of thesulfate additives resulted in, at best, only a small increase inalkaline citrate solubility over that obtained without additive.Regardless of when the sulfate was added, alkaline citrate solubilitiesranged, rather erratically, between about 40 and 60 percent. There wassome indication that solubility was highest (about 60 percent) when thesulfate was added at pH 2.5 during the ammoniation step. Although theseanalyses were made from 4 to 13 days after preparation of thesuspensions, analysis of similar suspensions by X-ray methods within 1hour after preparation showed that at that time about 65 percent of thetotal phosphate was already present as precipitated apatite and onlyabout 30 percent remained as dicalcium phosphate.

The pH of the suspensions was initially about 7 to 8. However, in mosttests the pH began to drop within an (CaO-SO4) hour of preparation andreached the range 5 to 6 during the first day of standing. Results oflater X-ray studies showed that this drop in pH correlated withreversion of dicalcium phosphate to fiuorapatite in the suspensions.

Referring now more specifically to FIGURE 7, a test (test 108) was madeto study further the action of a sulfate additive. In this test samplesfor chemical and X- ray analyses were taken at intervals throughout theammoniation step and the data are plotted in the manner used in examplessupra with and without phosphate additive. The chemical and X-rayanalyses shown were made 1 and 2 days, respectively, after preparationof the susoensions. Other X-ray analyses, not shown, were made only 30minutes after preparation.

It is apparent from FIGURE 7 that the presence of sulfate did notprevent formation of apatite. As in a previous test without additive(test 92) formation of apatite occurred in samples ammoniated to NH3ZNO3mole ratios above about 0.6 (NH :P O mole ratio, 4.0), which is thetheoretical point at which the precipitation of P as dicalcium phosphateshould be complete, according to the equation:

In extract 2NHa H PO XCa(NO3)2 In the sample ammoniated to the highestdegree (NH zNO mole ratio 0.93; initial pH 7.8) about 75 percent of theP 0 was in the apatite form 2 days after preparation (data in FIGURE 7).Only minutes after preparation (data not shown) about 63 percent of theP 0 had been converted to apatite. Neutral citrate solubility of the P 0remained 100 percent at all degrees of ammoniation, but alkaline citratesolubility was reduced drastically with ammoniation to NH :NO moleratios above about 0.6.

Other data in FIGURE 7 show that pH was unstable in samples ofsuspension ammoniated to initial pH above about 3. The pH of suchsuspensions began to drop shortly after preparation, dropped rapidlyduring the first day, and continued to drop slowly for about days. Thisresult indicates that the sulfate additive acted only to provide ashort-term delay in the conversion of dicalcium phosphate to apatite;such instability did not occur in suspensions without additive. Thisdelay in reaction was found, by X-ray studies, to favor the formation ofsmaller apatite crystals, which probably explains the effect of theadditive in increasing neutral citrate solubility. It is obvious fromthese results that use of the sulfate additive in contrast to use of anadditive selected from my group of reaction inhibiting materials, didnot provide a practical degree of inhibition of the reversion reaction(reversion of dicalcium phosphate to apatite).

Referring now more specifically to that portion of Table V that relatesto test 110, it is seen that a larger amount of sulfuric acid additivewas used in this test in order that the amount be suflicient to adjustthe CaO:P O mole ratio in the extract to 2.00, the ratio in dicalciumphosphate. It was of interest to determine whether such adjustment mightpreclude formation of apatite and thereby provide high alkaline citratesolubility. The amount of sulfuric acid (93 percent H 80 required wasabout 250 pounds per ton of suspension; this was mixed with the nitricacid prior to extraction. Grade of the suspension was only about 990 asa result of dilution by the acid and by the water was required tomaintain fluidity during ammoniation.

X-ray analyses made immediately after preparation of the suspensionindicated that 78 percent of the P 0 was present as dicalcium phosphateand 8 percent as apatite. On standing, the proportion of apatiteincreased to 24 percent during the first day and to about 40 percentduring the first week. Chemical analyses, made after 1 week of standing,indicated high neutral citrate solubility (about percent) but only 64percent alkaline citrate solubility. Water solubility of the P 0 was 6percent. Results of this test indicate that even full dajustment ofCaO:P O ratio with sulfuric acid did not provide the desired stablesuspension of high alkaline citrate solubility. Also, physicalproperties of the suspension were unsatisfactory even with dilution tothe 990 grade.

In a previous example, comparison tests were reported in which 15percent of the total P 0 was furnished as orthophosphoric acid orammoniated orthophosphoric acid. The results showed that this amount oforthophosphoric acid, which was sufiicient to adjust CaO:P O mole ratioonly to 3.05, did not improve the alkaline citrate solubility of neutralsuspensions, whereas the same proportion of P 0 as 1l370 ammoniatedsuperphosphoric acid (70 percent polyphosphate) was highly effective. Anadditional test (test 111) with orthophosphoric acid additive will nowbe described in which the proportion of phosphoric acid used wassufiicient to adjust CaO:P O mole ratio to 2.0. The amount of acidrequired accounted for 45 percent of the total P 0 in the suspension. Itwas of interest to determine whether such adjustment would providestable neutral suspension of high alkaline citrate solubility. Data fromthis test are included in Table V, infra.

X-ray analyses made 30 minutes after preparation of the suspensionindicated that 92 percent of the P 0 was present as dicalcium phosphateand that there was no apatite present. After 7 days of standing, 86percent of the P 0 was indicated to be present still as dicalciumphosphate and only 5 percent as apatite; however, chemical analysis atthis time showed only about 78 percent solubility in alkaline citrate.Reasons for the discrepancy between the X-ray and chemical analyses arenot known. On further standing for 42 days total, the proportion of theP 0 found as apatite by X-ray analysis increased to 13 percent. Furtherchemical analyse-s were not made. The overall conclusion from this testis that full adjustment of CaO:P O mole ratio with orthophosphoric acidprovided a fairly stable suspension of rather low apatite content. Sucha suspension, however, would have a relatively small economic advantage,because of the high proportion of phosphoric acid required.

Tests with magnesium additive A nitric phosphate suspension containingmagnesium sulfate additive was prepared and included in a series ofgreenhouse tests. Neutral citrate solubility of this suspension washigh, but alkaline citrate solubility was not determined. Results of thegreenhouse tests were poor. Later two further exploratory tests weremade the results of which indicate that magnesium is not effective inproviding high alkaline citrate solubility in nitric phosphatesuspensions.

In the later tests, magnesium nitrate was used as the additive insteadof the sulfate in order to eliminate effects of the sulfate ion and thusmake the test specific in regard to magnesium. The additive wasdissolved in water and added to the suspension after ammoniation hadprogressed to about 2.4. In one test, the proportion of additive wassuch as to provide Mg:P O mole ratio of 0.145, which was the proportionused in the suspension that was tested previously in the greenhouse. Inthe other of the tests, the proportion of additive was doubled.Identical results were obtained with both levels of magnesium. Neutralcitrate solubilities were 95 percent and alkaline citrate solubilitieswere only 46 percent.

TABLE V.PREPARATION OF NITRIC PHOSPHATE SUSPENSION FE RTILIZERS BY BATCHAMMONIATION WITH SULFATE AND ORTHOPHOSPHATE ADDITIVES Test Number 92 10870 80 94 110 111 Tests with full adjust- Tests with small amount e ofsulfate additive ment of CaOzPzOs mole ratio to 2.0

Additive N n H2304 (NH4)2S04 b HzSO4 H3130;

Immedi- Immedi- With ately after ately after With With when added HNO;extraction extraction pH 2.2 HNO HNO Formulation, lb./ton of P205111product:

Phosphate rock r 6,060 6. 060 6. 060 6, 060 6,060 6, 060 3, 340 Nitricacid (42% HNOa) 14, 340 14, 340 14, 340 14, 340 14, 340 8, 458 7, 380Additives:

Sulfuric acid (93% H2604) 569 569 0 0 2, 438 0 (NH4)zS04 (100% basis) b0 0 0 716 716 0 0 Orthophosphorie acid (86% HaP04) 0 0 0 0 0 0 1, 450Ammonia (gaseous anhydrous) d 1, 526 1. 479 1,527 1, 706 1, 576 1,259984 Water I! (to maintain fluidity) -2, 726 2, 648 2, 696 622 692 +655-1, 534 Extraction:

HNO ;CaO mole ratio 1. 86 1. 86 1. 86 1. 86 1. 86 1.10 1 86 (HNO+2HrSO4) :CaO mole ratio 1 2. 07 2. 07 2.00 Time, min 20 20 20 20 20 20Ammoniation:

09.01 105 mole ratio 3. 64 3. 64 3. 64 3. 64 3. 64 3. 64 c 2, 00(CaO-SOU P205 mole ratio (after addition of sulfate dditive) 3. 28 3. 283. 28 3. 28 2.00 H Final NHazI-INOs mole ratio 4 0. 91 0. 94 1. 050.97 1. 31 1. pH at end of ammoniation .0 7. 8 8.4 8.1 8.1 7.7 7. 7 pHafter 1 day .4 5. 0 4. 3 8.0 5. 2 7. 6 7. 5 Storage time prior toanalysis, 1 13 13 7 13 7 6 Chemical analysis of final suspension 12.812. 6 13. 6 12. 6 12.2 9.0 12.8 6.2 6.0 6.6 6.4 6.0 5.1 6.8 10. 4 10. 110. 1 9. 0 9.1 10.6 16. 5 Neutral citrate-soluble P205 8. 3 9.8 9. 8 9.0 8. 7 9. 5 16. 3 Alkaline citrate-soluble P205. 3. 5 5. 8 5. 7 3. 7 5.16.8 12. 8 Water-soluble P105 0 8 0- 3 0. 1 0. 3 0. 6 2. 0 Total OaO 1 614- 6 13. 3 13. 2 15. 4 13. 3 s0 2. 9 2. 7 2. 7 P205 solubility, percentof total P 0 Neutral citrate (A.O.A.C.) 80 97 97 100 96 90 99 Alkalinecitrate 34 57 62 41 56 64 7 8 Water soluble 0 8 3 0 3 6 12 Phy siggl prgperties of suspension (after standing 1 day at Apparent viscosity,centipoises 5 8 1,01 135 530 1, 340 430 Settled, percent 7 0 0 0 1 1Pourability, percent l Sulfate proportion equivalent to about 60 poundsof 93% H2804 per ton of suspension.

b Reagent grade; added as 36% solution.

a Florida floatation concentrate: 33.0% P205, 47.5% 08.0; minus 10-giiifritity calculated from NHazNOs ratio in final slurry.

* Net addition or loss of water; calculated from P205 balance.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. In the production of nitric phosphate fertilizers wherein particulatephosphate rock is extracted with nitric acid to form a fluid slurry ofnitric acid-phosphate rock extract, which fluid slurry is subsequentlyammoniated to a terminal pH in the range from about 6 to about 8 toyield a resulting ammoniated nitric acidphosphate rock fluid slurry foruse as nitric phosphates and nitric phosphate suspensions, theimprovement wherein the nitric acid-phosphate rock fluid slurry istreated prior to the ultimate terminal ammoniation thereof to ensure a P0 solubility in both neutral citrate and alkaline citrate of greaterthan about 90 percent in the ultimate product, said improvementcomprising contacting said nitric acid phosphate rock fluid slurry whiles aid fluid slurry is in the pH range of about 1.9 to about 2.5 with areaction inhibiting material in quantity sufficient to supply in therange from about 10 percent to about percent by weight of the total P 0content in the nitric phosphate fertilizer material produced, saidquantity of reaction inhibiting material being sufiicient to inhibit theconversion to apatite of the soluble calcium in the nitric phosphatefertilizer produced, said reaction inhibiting material characterized byits ability to yield in solution with said nitric acid-phosphate rockfluid slurry acyclic polyphosphate anions and said reaction inhibitingmaterial selected from the group of polyphosphates consisting ofammonium, sodium, potassium, calcium, magnesium, and mixtures thereof;thereafter completing the ammoniation of the nitric acid-phosphate rockfluid slurry extract to the terminal range of about 6 to about 8 wherebythe calcium phosphate content in the resulting ammoniated f Effectiveacidulation ratio based on assumption that H2804 reacts with rock toform CaSO4.

1; After addition of phosphoric acid.

11 Includes water-soluble P205.

i Brookfield viscometer at 100 rpm.

Clear layer, percent of total volume.

Percent pourable in 1 min. from qt. jar tilted 45. nitric acid-phosphaterock slurry is substantially completely in the form of dicalciumphosphate.

2. An improved process according to claim 1 wherein said reactioninhibiting material is a stable solution of ammonium salts of acyclicpolyphosphoric acid.

3. An improved process according to claim 2 wherein said stable solutionof ammonium salts of acyclic p'olyphosphoric acid contains in the rangefrom about 11 to 15 percent nitrogen and 33 to 45 percent phosphorus,said phosphorus [expressed as P 0 4. An improved process according toclaim 1 wherein said reaction inhibiting material is sodiumtripolyphosphate.

5. In the production of nitric phosphate fertilizers wherein particulatephosphate rock is extracted with nitric acid to form a fluid slurry ofnitric acid-phosphate rock extract, which fluid slurry is subsequentlyammoniated to a terminal pH in the range from about 6 to about 8 toyield a resulting ammoniated nitric acidphosp'hate rock fluid slurry foruse as nitric phosphates and nitric phosphate suspensions, theimprovement wherein the nitric acid-phosphate rock fluid slurry istreated prior to the ultimate terminal ammoniation thereof to ensure a P0 solubility in both neutral citrate and alkaline citrate of greaterthan about percent in the ultimate product, said improvement comprising:

(1) introducing a stream of fluid slurry of nitric acidphosphate rockextract and a stream of ammoniating fluid into a first reactor, andadjusting the relative proportions of said nitric acid-phosphate rockextract and ammoniating fluid to maintain the pH in said first reactorin the range from about 1.9 to about 2.5;

(2) simultaneously introducing into said first reactor a stream ofreaction inhibiting material in quantity sufficient to supply in therange from about 10 percent to about 20 percent by weight of the total Pcontent in the nitric phosphate fertilizer material produced, saidquantity of reaction inhibiting material being sufiicient to inhibit theconversion to apatite of the soluble calcium in the nitric phosphatefertilizer produced, said reaction inhibiting material characterized byits ability to yield in solution with said nitric acid-phosphate rockfluid slurry acyclic p'olyphosphate anions and said reaction inhibitingmaterials selected from the group of polyphosphates consisting ofammonium, sodium, potassium, calcium, magnesium, and mixtures thereof;

(3) subsequently simultaneously introducing a stream of the resultingmixture of partially ammoniated nitric acid-phosphate rock fluid slurryextract, and said reaction inhibiting material from said first reactorinto a second reactor, together with a stream of ammoniating fluid;therein intimately mixing said material introduced; controlling the rateof introduc tion of said ammoniating fluid into said second re actionvessel to maintain the acidity therein in the range from pH 6 to aboutpH 8; and

(4) withdrawing from said second reactor the resulting nitric phosphatefertilizer wherein the calcium phosphate content is substantiallycompletely in the form of dicalcium phosphate.

6. An improved process according to claim 5 wherein said reactioninhibiting material is a stable solution of ammonium salts of acyclicpolyphosphoric acid.

7. An improved process according to claim 6 wherein said stable solutionof ammonium salts of acyclic polyphosphoric acid contains in the rangefrom about 11 to 15 percent nitrogen and 33 to percent phosphorus, saidphosphorus expressed as P 0 8. An improved process according to claim 5wherein said reaction inhibiting material is sodium tripolyphosphate.

References Cited UNITED STATES PATENTS 2,738,265 3/1956 Nielsson 71-43XR 2,861,878 11/1958 Bigot 71-39 3,015,552 1/1962 Striplin et al. 7143XR 3,050,384 8/1962 Bigot 7139 3,264,087 8/1966 Slack et a1 71-43 S.LEON BASHORE, Primary Examiner B. H. LEVENSON, Assistant Examiner US.Cl. X.R. 71-43; 23109

